nfsd4: move principal name into svc_cred

Instead of keeping the principal name associated with a request in a
structure that's private to auth_gss and using an accessor function,
move it to svc_cred.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index c8e9f63..a5fd6b98 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -650,9 +650,10 @@
 	struct rpc_clnt *client;
 
 	if (clp->cl_minorversion == 0) {
-		if (!clp->cl_principal && (clp->cl_flavor >= RPC_AUTH_GSS_KRB5))
+		if (!clp->cl_cred.cr_principal &&
+				(clp->cl_flavor >= RPC_AUTH_GSS_KRB5))
 			return -EINVAL;
-		args.client_name = clp->cl_principal;
+		args.client_name = clp->cl_cred.cr_principal;
 		args.prognumber	= conn->cb_prog,
 		args.protocol = XPRT_TRANSPORT_TCP;
 		args.authflavor = clp->cl_flavor;